Japanese Non-examined Patent Publication No. 2002-148711 discloses a virtual space creation system. This virtual space creation system is intended to immerse an observer in a virtual space with the use of a curved screen giving a wide field of view for image projection.
In order to give immersion to several observers at the same time, a large screen is needed. Japanese Non-examined Patent Publication No. 2001-306024 discloses a system for projecting images on a large screen. In this invention, the system divides a single seamless image into a plurality of divided images, and projects the divided images on a large flat screen from a plurality of projectors. Each of the divided images is projected on the flat screen with adjacent ones of the divided images partially overlapped so as not to produce a clearance between the divided images. Since overlapping areas which overlap between the adjacent divided images have high-brightness, the overlapping areas appear to be bright on the screen. To solve this program, a brightness filter is used. The brightness filter lowers the brightness of the overlapping areas of each of the divided images according to an overlapping amount between divided images. Each of the divided images is projected on the flat screen after the brightness of its overlapping area is lowered by the brightness filter. In this way, this system can obtain a seamless combined image in which the brightness of the overlapping areas is in harmony with the brightness of non-overlapping areas.
In above-mentioned invention, because of a flat screen, the images are projected on the flat screen without being distorted. Therefore, it is easy to calculate overlapping areas of divided images and create brightness filters beforehand, if a positional relationship between the projector and the screen, a shape of the image projected from the projector, etc. are known.
However, if the screen is a curved screen, it is very difficult to calculate overlapping areas of each of the divided images and create brightness filters beforehand, because each of the divided images on the screen is distorted.